Yes, Cassie does

You try your best to hold back, but everytime you get slower, nyx instantly commands you to go faster again. So close to an orgasm yourself, you try to just focus on the strap-on. You try to tell yourself that this isnt your cock fucking your girlfriend, so you shouldnt feel the need to cum.
That you´re not the only one struggling to last is something you remember too late.

With a muffled moan, your girlfriend cums on the fake cock. You see her legs quiver, but out of surprisement you pull back, and the strap-on glides out. With your hands still cuffed you cant put it back in, and so you just have to watch as your girlfriend suffers under an ruined orgasm.
Cassies moans are **** as her body shakes under her orgasm that doesnt give her any satisfaction. It takes a couple of moments before she catches her breath again.

You feel like you see a slight satisfied smile on Nyx´s face, but as you look again her expression is cold.

She moves away from Cassie, who is still on her knees bend down in front of you. The strap-on hangs above your own dick, covered in your girlfriends juices.

As Nyx speaks, her voice is cold. "What did I tell you?"

"Not to cum unless you tell us to, but-"

"Do not speak back to me."

You fall silent, your heart races. You feel humiliated and almost a bit afraid, but also...really, really turned on. Your cock still twitches a bit, but without the stimulation, you feel yourself moving away from the edge.

Nyx comes over to you and removes the strap on, leaving you naked again, your now semi-errect cock hanging between your legs as you kneel.

Nyx grabs your girlfriends shoulder and pulls her back up on her knees. She turns her around to face you. Cassie seems a bit dazzled, the two of you look at each other and blush. You feel like just the sight of her is enough to make you fully hard again. You are both handcuffed, exposed to your misstress, helpless, and you loved it. Cassie looks beautiful and for a second you forget everything around you. Not for long though, as Nyx pulls you back to reality.

"So even with the experience the two of us have together, you couldnt help but be selfish and cum."

You wonder what Cassie thought. She looked embarassed, and still a bit out of breath.

"Now, I told you not to cum, but one of you did. You want to submit to me as a couple, and so I am going to punish you as a couple."

You hold your breath as you wait for Nyx to tell you what punishment she has in mind.